vol 9, issue 2

Biomimicry - the next engineering revolution?

10 February 2014
By Christine Evans-Pughe
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A curled leaf

Learning from birds and bees

Jay Harman

‘The growing cost of energy alone is a good reason to look to the natural world for new solutions’

Jay Harman’s impeller

Modelled on spirals found in shells and whirlpools, this impeller is used for mixing layers of stagnant water

A close-up of a tardigrade in moss

Tardigrades are lending their survival abilities to UK firm Nova Laboratories

A close-up of a cat's claw

The Bath team used a cat’s paw to model how a car tyre needs to change in icy conditions

The natural world and its inhabitants are expert at developing energy-efficient and flexible designs. Engineers can learn a lot from Mother Nature's survival processes.

For millions of years nature has carried out trillions of trial and error experiments, which is why its successful designs are more energy efficient and flexible than anything humans have dreamt up.

Now that we have the technology to analyse, simulate and assemble biological materials from the molecular level up, there are those who say we are on the brink of an engineering biomimetic revolution. If so, engineers and technologists need to adjust to a new multi-functional, evolutionary, endlessly recyclable way of thinking.

Earthworm-inspired artificial muscles, aerodynamic paint that mimics shark skin, and vaccines preserved by a sugar found in moss piglets, are just a small selection of intriguing biomimetic ideas explored by Australian-born inventor and entrepreneur Jay Harman in his new book 'The Shark's Paintbrush: Biomimicry and How Nature is Inspiring Innovation'. Harman is a keen advocate of biomimicry, pointing out that the growing cost of energy alone is a good reason to look to the natural world for new solutions.

His own nature-inspired inventions are a case in point. One is an impeller, modelled on spirals found in shells and whirlpools, for mixing layers of stagnant water in huge municipal water tanks. "Instead of needing two tanks and pumping water from one to the other, the mixer can circulate the water in a single tank using 90 per cent of the power while also reducing the amount of chlorine by 80 per cent," he explains.

Exciting as such ideas are on paper, turning nature into technology is not straightforward and promising ideas can end up as mere gizmos. Take Velcro, an iconic piece of biomimicry based on the hooks found on burrs. It has been around for 50 years but has not generated an engineering revolution, just easy-fastening shoes for toddlers and the elderly.

Truly successful biomimetics requires a deep understanding of how natural systems work and a new design approach, argues zoologist Julian Vincent who has written extensively on biomimicry and spent eight years as a professor of mechanical engineering at the University of Bath teaching engineering students to apply these ideas.

Engineering, he points out, is numerical, solves tightly defined problems and - if done properly - has predictable, reliable solutions. The best engineering ideas are nailed down with a patent. Biology, in contrast, is open-ended, full of surprises and its successful ideas are shared. Because biology spreads its successes using genes and overwhelms the opposition with improved survival, we can often only guess at the particular problem one organism is solving because each one adresses a wide range of survival issues. To try to square this circle, Vincent and colleagues developed a method called BioTriz, which can frame a problem and solve it in novel ways by helping to transfer ideas from nature to engineering.

Materials are expensive and design is cheap

Usefully, biological materials generally derive from just two polymers – protein and polysaccharide – plus crystalline materials that are mostly calcium-based. From these simple beginnings, they have mechanical properties (taking density into account) covering much the same range as metals, ceramics and the 300 or so widely used manmade polymers.

Insect cuticle, for example, can vary in stiffness over seven orders of magnitude from something as soggy as thick mucus to over 10 GPa (gigapascal) in the mandibles of plant-eating insects. Michael Ashby, principal investigator at the Engineering Design Centre Cambridge University, and Ulrike Wegst, now associate professor of engineering at Dartmouth College in the USA, undertook this analysis a few years ago, finding that high-performance metal matrix composites and some specialist ceramics were the only exceptions.

Natural materials get these diverse mechanical properties from varying the size, shape, proportion, distribution and orientation of different elements. Or as Vincent puts it, in biology "materials are expensive and design is cheap". Design in biology, he points out, starts at the molecular level of information transfer, i.e. the genetic instructions, which tease highly efficient structures from the organism's surroundings using the least resource.

"Mother-of-pearl, the stuff of shells, is a good example. It is 3,000 times tougher and more durable than a homogenous lump of its main ingredient chalk [calcium carbonate]", Vincent says.

Claus Mattheck, of the Institute for Materials Research at Karlsruhe University, who developed efficient structures from measuring and modelling trees, has shown that simply changing the shape of a curve around a corner can improve the durability of an object by factors of a million or more. More effective shapes require less material.

Michael Pawlyn, director of the London-based architectural practice Exploration (and lead architect of the Eden Project), has been using these insights about materials in a number of buildings. The Wood Green Animal Shelter Education Building design, for example, uses shape to create robust structures with a minimum of materials. It is based on a timber grid-shell built entirely out of small sections of timber. It achieves the strength necessary through its curved forms that create stiffness with a minimum of materials.

Pawlyn's team has even been examining bird skulls to help develop more efficient floor slabs for office buildings and to make thin curved glazing systems. A magnified crow or magpie skull shows multiple bony shells connected by a matrix of ties and struts, delivering material efficiency through its stiff shape with an inner structure subdivided for strength, as Pawlyn explains in an article published in Nature in February 2013, co-authored by Olympic Velodrome engineer Chris Wise and the chemist Michael Braungart.

Mass-produced spiders

In the same article, Pawlyn predicts that in the next few decades it should be possible to use natural, endlessly recyclable polymers such as the polysaccharide-based cellulose, found in wood, or chitin, a component of insect and shellfish exoskeletons. Computer-aided design and simulation, 3D printing, and nanotechnologies are already helping us to produce some of the complex materials, structures and shapes found in plants and animals. But there is further to go.

Clues as to how we might produce biomimetic materials in quantity come from David Knight at Oxford Biomaterials Ltd, who is working on liquid crystals including spider silk. Many biological materials are liquid crystalline in origin including muscle and collagen. Unlike manmade liquid crystal fibres such as Kevlar, which are single stiff molecules relying on the stability of the strong primary chemical bonds and little else, biological ones are made from very weak primary bonds (collagen, for example, is stabilised by hydrogen bonds).

Such construction is cheap in terms of energy but has a pre-self-assembly stage, which means the liquid crystalline structure is two steps down the road of hierarchy, which brings greater stability and strength.

The polypeptides that make up spider silk assemble themselves into liquid crystal form in the creature's spinneret ducts. The stretching of the silk as it comes out then orientates the polypeptide sub-units and locks them all together. "The degree of stretching, which is something you find in extruded polymers too, controls the crystals' orientation. If you have a low extension ratio, you have less crystallinity and more rubbery silk. If you have a high extension ratio you get stiffer silk," explains Vincent.

Using the spider spinneret analogy, extrusion-based rapid prototyping could be used to produce high-performance fibres in a similar way. An alternative approach might be a system where the materials either set on contact with (for example) calcium ions in a mass of water within which the object is being made, and/or use water-based interactions to self-assemble on a surface as they are extruded. Post-processing would get rid of excess water rather as insects do when they stiffen their outer shell.

No eco guilt-tripping

All this bodes well for a form of nature-inspired manufacturing in which all the materials used must be beneficial as biological nutrients that can re-enter our water or soil, or as 'technical nutrients' such as copper that can continually circulate in closed loop industrial cycles.

Known as cradle-to-cradle, it was first conceived by chemist Braungart in his Environmental Protection Encouragement Agency (EPEA) in the late 1980s. Today, cradle-to-cradle is used by 200 or so organisations including sports clothing firm Puma, cosmetics company Aveda, cleaning materials company Method, and furniture maker Orange Box. It is also the subject of an influential new book 'The Upcycle: Beyond Sustainability - Designing for Abundance' by architect William McDonough and Braungart, with a forward by Bill Clinton.

Braungart sees everything as nutrition and the 'carbon neutral, zero waste, zero footprint' mantra as nothing but tiresome guilt management. "Why are all other species beneficial but the best thing for humans is there should be fewer of us?" he asks. "Did you ever see a tree minimise its carbon footprint? The biomass of ants is much larger than humans; they only live three to six months and work much harder physically than we do, they are the equivalent of 30 billion people in their calorie consumption."

Cradle-to-cradle innovations range from mushroom packaging that replaces polystyrene foam to carpets that make the air cleaner air in the home. Sixty per cent of airline upholstery is now made of edible fabrics using the cradle-to-cradle approach. Appropriately, 'The Upcycle' is the first book with paper, pigments and optical brighteners suitable for composting or burning thanks to printing company Gugler's cradle-to-cradle process. "If you burn any magazine or newspaper, it is so toxic it cannot be used by biological systems," says Braungart.

Book burning doesn't have a happy history and is unlikely to be the response to any kind of engineering revolution. But in the event that some crazy group takes exception to these life-affirming ideas, it will at least be beneficial for the planet, jokes Braungart.

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Development: Tardigrade in Moss

Moss piglets, or tardigrades, are microscopic creatures notable for their ability to survive in extreme conditions including outer space. The tardigrade's trick of living in suspended animation for years by replacing water in cells with a sugar called trehelose, is now used by the UK firm Nova Laboratories as a way of preserving vaccines without refrigeration - crucial in developing countries where vaccines are a matter of life or death and electricity supplies are typically unreliable.

BioTRIZ: Thinking your way towards biomimetics

Asked to design an anchor, most of us will produce a variation of Popeye's famous tattoo. Asked to stabilise a boat given a fridge and GPS, we will think more imaginatively. A fridge's function is freezing so a creative (albeit impractical) answer is to freeze the sea. GPS, on the other hand, could keep the boat stable with accurate positioning.

These examples show how the Triz method, developed by Soviet inventor Genrich Altshuller, can help solve a problem with inventions from other fields of engineering. BioTriz is a variation developed by zoologist Julian Vincent and colleagues at the University of Bath for transferring ideas from nature.

"At the heart of this is thesis and antithesis; you don't get a problem unless there is an obstacle," says Vincent. Problems are constructed out of pairs of opposing characteristics ('what do I want' and 'what is stopping me') that become the vertical and horizontal axes of a matrix. By analysing 500 or so biological phenomena, the team developed a list of 2,500 conflicts and resolutions. The solutions whose conflict pairs closely match those of the problem under examination are then used as analogues of the solution sought and put in the matrix.

One example is a tyre changing in icy conditions. This presents a typical conflict as it needs to be soft and smooth yet solid, hard and sharp. A functional biological prototype could be a cat's paw with claws that can be withdrawn. The solutions from nature are: Segmentation - the paw is split into several pads and claws; Local quality - the paw is only sharp at the operating zones of the claws; Spheroidality or curvature - the pads are spheroidal, the claws are curved; and Dynamics - the claws can be deployed or retracted at will.

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